linux-kernel - [ 33/50] ipc,shm: shorten critical region in shmctl

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Message-Id: <20131016174402.341337598@linuxfoundation.org>
Date:	Wed, 16 Oct 2013 10:45:19 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Davidlohr Bueso <davidlohr.bueso@...com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <efault@....de>
Subject: [ 33/50] ipc,shm: shorten critical region in shmctl_down

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <davidlohr.bueso@...com>

commit 79ccf0f8c8e04e8b9eda6645ba0f63b0915a3075 upstream.

Instead of holding the ipc lock for the entire function, use the
ipcctl_pre_down_nolock and only acquire the lock for specific commands:
RMID and SET.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Manfred Spraul <manfred@...orfullife.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/shm.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -787,11 +787,10 @@ static int shmctl_down(struct ipc_namesp
 	down_write(&shm_ids(ns).rw_mutex);
 	rcu_read_lock();
 
-	ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
-			       &shmid64.shm_perm, 0);
+	ipcp = ipcctl_pre_down_nolock(ns, &shm_ids(ns), shmid, cmd,
+				      &shmid64.shm_perm, 0);
 	if (IS_ERR(ipcp)) {
 		err = PTR_ERR(ipcp);
-		/* the ipc lock is not held upon failure */
 		goto out_unlock1;
 	}
 
@@ -799,14 +798,16 @@ static int shmctl_down(struct ipc_namesp
 
 	err = security_shm_shmctl(shp, cmd);
 	if (err)
-		goto out_unlock0;
+		goto out_unlock1;
 
 	switch (cmd) {
 	case IPC_RMID:
+		ipc_lock_object(&shp->shm_perm);
 		/* do_shm_rmid unlocks the ipc object and rcu */
 		do_shm_rmid(ns, ipcp);
 		goto out_up;
 	case IPC_SET:
+		ipc_lock_object(&shp->shm_perm);
 		err = ipc_update_perm(&shmid64.shm_perm, ipcp);
 		if (err)
 			goto out_unlock0;
@@ -814,6 +815,7 @@ static int shmctl_down(struct ipc_namesp
 		break;
 	default:
 		err = -EINVAL;
+		goto out_unlock1;
 	}
 
 out_unlock0:


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